Low-water thermal cutoff for steam generators



March 6, 1951 E. w. HENKEL 2,544,384

: LOW-WATER THERMAL CUTOF'F FOR STEAM GENERATORS Filed Oct. 18, 1948 I i P I: U f 4 W 4 ,4/ 2 8 a4- j i 2s l3 I 5 32 2a J 0 0/4 Baku: com-R0 R Ewan W HENKEL INVENTOR.

Patented Mar. 6, 1951 UNlTEl) STATES PATENT OFFICE.

LOW-WATER THERMAL CUTOFF FOR STEAM GENERATORS Erich W. Henkel, Calumet City, 111., assignor to Combustion Engineering-Superheater, Inc.,

New York, N. Y.

' Application October 18, 1949,"Serial No. 121,984

- f 3 Claims. (Cl. 122-504) 1 The present invention relates to protective devices particularlyfor steam boilers to prevent overheating or burning of tubes through which I the fluid to be heated and vaporized is circulated.

of the furnace arelined'with-radiantly heated tubes which lie relatively close to theburning products of combustion in the furnace and-momentarily contain only relatively small amounts of water. Consequently, if the supply of water to these tubes becomes inadequate, or ,fails completely, the'tubes are exposed to the danger of becoming overheated or even burning out with consequential disablin of the steam generator.

Heretofore, safety devices have been provided in boilers which react to changes in pressure conditions therein or to the rate of flow in the tubes. However, with a boiler whose tubes momentarily contain only a small amount of water it is desirable to provide protective apparatus which will be responsive to the actual temperature conditions to which the tubes are exposed.

The invention will be best understood upon consideration of the following detailed-description of an illustrative embodiment thereof when read in conjunction with the accompanying drawings in which:

Figure 1 is a vertical section in diagramatic form of a steam generator provided with a protective system embodying the present invention,

and

Figure 2 is a diagram of an electrical control circuit.

The steam generator illustrated in Figure 1 has a U-shaped gas passage, one leg of which forms a furnace chamber l downwardly fired by fuel burner means H. The furnace l0 communicates through an outlet ill in its inner side wall at the lower end thereof with the adjacent convection passage l2 from the upper end of which spent gases pass to a stack l 4. The walls of the furnace chamber ID are lined with radiantly heated steam generating surface comprising several steam generating coils 2| each of whose successive tube convolutions are superimposed in vertically spaced relation to form a generally spiral path for fluid flow. The convection coils are connected to receive a supply of water from a horizontal, generally U-shaped'supply header 25 that extends along the three outer sides of the convection passage l2 at the top of the rectangular shaped generator at the left hand end thereof. The various convolutions of the coils 2| have fins 24 thatfill the spaces between the tube convclutions and provide substantially solid walls bounding the combustion chamber. The parts of the coil convolutions on the inner side of the combustion chamber ll! form a wall dividing it from the convection passage l2. Alternate convolutions of the lowermost coil extend into the convection passage l2 and lie against its outer walls as at '23, thespacing of these convolutions providing openings that form the gas outlet [3.

The steam generating surface in the convection passage l2 consists of several coil units, of which the one shown in Figure 1 is designated 30, each made up of parallel tube lengths serially interconnected for fluid flow by return bends. The various convection coils are also connected to the water inlet header 25.

A'Ihemixture of steam and water from all the radiant and convection coils is discharged into an outlet or collecting header 26 from which it passes into the separating drum 28 through a pipe 21. The separatedwater flows through downcomer 29 to the inlet of the forced circulation pump, 32 which supplies the inlet header, 25 through piping 36, 31.

For the purpose of afiording protection against overheating the steam generating tubes, a pilot tube designated as awhole by the numeral 40 is provided which extends into the furnace adjacent the burners l I so as to be exposed to the temperature conditions existing therein. This pilot tube should be made of high grade steel to withstand high temperatures. In the construction shown the pilot tube 40 resembles a so-called "field tube consisting of an outer tube 4| connected by a pipe 42 to the pipe 36 so that it may receive water from the delivery side of the circulation pump 32. Within the tube 4| is a second tube 43 extending from a point above the bottom thereof to project from the opposite end 44 so that it may be connected to a pipe 45. The pipe 45 carries ofi the water circulated through the pilot tube 40 as for example by connecting it with the steam and water collecting header 26. Located within the pilot tube 4|] so as to be exposed to the temperature of the water flowing through it is a thermally responsive element which is associated with a switch 53 and arranged plus some. with n me so as to open an electric circuit 64, 65, Fig. 2, that governs the operation of the pump for supplying fuel to the burners I I, this occurring when the temperature in tube 40 exceeds a predetermined value. In Fig. 2 there is indicated a pressure responsive thermal device 59 which when an excess of pressure is reached produces expansion of the bellows 60 through element 62 to open the switch 63 in the circuit 64, 65 from which the motor 66 of the fuel burner pump 51 is operated. The switch 53 has contacts arranged in the circuit 64, 65 so that when the thermal element 59 reacts to excessive temperature conditions within the pilo tube 40 the switch is opened so as to cause the fuel pump to be shut down.

The pilot circuit is expos d to thefurnace heat so that even at low loads a fairly high heat absorption rate can be assured. Flow conditions and heat absorption rates for the pilot circuit can be calculated so that ample water circulation exists when conditions are at normal; yet,

should the generator begin to run dry, the pilot tube will starve first. The thermal device is set so that an overheating of this pilot circuit above normal causes the device to open the switch 53.

Interposed in the pipe 42 between the delivery side of the suction pump 32 and the pilot tube 40 is a shut-01f valve 4'! which permits the thermal device to be tested without shutting down the generator. -Heretofore safety devices ac ua by res u or t r flow ond on w re often rred ec e t ei per orman cou d be t s ed whi the nera or oper ting- In o h w rds it su h. d ice it is not neces- T4 Fy to u off he fe d wa r nd mm h e erator dry in order to test the reactionof a presure sa e e i ch as ha ind c a T is te c ld be ri d, out'bv s ni ly op n ng a te val e i ed n a ble -off l ne whic would carry off enough water from the, generator so as to dire l re duce. red ced pressure o l w c t n whi h would ex s when d ng arose. A safety device actuated by temperature ha n t e o s dered e able in the past ec use. o h d fiiculnes enco n ered in testi the a tio o he ermal de ic hi e the gen rato i w king und r normal co di io s- "lhje amount of water diverted'throug'h the pilot tube!" s im t d by es rictins th flow n p p 42. This may be don b actu l y res ric ng th internal flow area of pipe '42 .as diagrammatically indica ed n Pia. l th ough iorni o v stri'c i n o ts nterna diam t n actualnsaot c ithis would efe ably is, y us of s provided with a smaller orifice or bore. Alternatively, the restriction to flow might occur due to only partial opening of the valve 41. With the pilot tube of the present invention receiving a small part of the water circulated through the generator by the recirculation pump continuous protection is afforded and italso becomes possible by closing valve I! to obtain a-reliable test of the safety device without shutting down the boiler or taking it out of normal operation. Overheatin OI the pilot circuit takes place on closing valve, 41 and the thermal device 50, 53 comes into action.

What I claim is:

1. In a forced circulation boiler having a furnace, means for introducing fuel to and burning it in said furnace steam generating elements exposed to the heat of products of combustion from fuel burned in said furnace, and a pump connected to said steam generating tubes for supplying water under pressure thereto; a pilot tube "disposed so as "to be exposed to the heat of fuel burned in said furnace; piping connected to the delivery side of said pump and to said pilot tube and so arranged as to pass part of the water delivered by said pump through said pilot tube while said pump is in operation for supplying water to said generating elements; a thermally responsive element associated with said pilot tube and means subject to said thermal means for controlling the operation of said burner.

13., In "a protective system for a forced circulaon boile as s eci d in claim 1: a no ma ly open shut -oii alve. nterpo d. n sa d p pin in loca ion betw en .said P mp and p t. be adapted wh n closed du ing operation of said boilerto deprive .said pilot tube of water so as o t s the ii cion y of aid. h rma means.

:In a [prote ive sy tem or a f r c rculation boilera s e ified. n cla 1; a restr tion sai pipin 1.11 a locat on etween said pump and pil tu fo limi n the amoun o wa owingthroueh thelatter to a limited pr portio of. e delivery of sa d. pump.

nron w. HENKEL.

REFERENCES CITED The following references are of record. .in the file or th s patent:

UNI-IEQSTATES manure, 

